File: gawk.info,  Node: Truth Values,  Next: Typing and Comparison,  Up: Truth Values and Conditions

6.3.1 True and False in 'awk'
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Many programming languages have a special representation for the
concepts of "true" and "false."  Such languages usually use the special
constants 'true' and 'false', or perhaps their uppercase equivalents.
However, 'awk' is different.  It borrows a very simple concept of true
and false from C. In 'awk', any nonzero numeric value _or_ any nonempty
string value is true.  Any other value (zero or the null string, '""')
is false.  The following program prints 'A strange truth value' three
times:

     BEGIN {
        if (3.1415927)
            print "A strange truth value"
        if ("Four Score And Seven Years Ago")
            print "A strange truth value"
        if (j = 57)
            print "A strange truth value"
     }

   There is a surprising consequence of the "nonzero or non-null" rule:
the string constant '"0"' is actually true, because it is non-null.
(d.c.)